1. Field of the Invention
The present invention is directed to improvements in capacitors of the multi-layer ceramic type (MLC). It is conventional in electronic devices such as computers, television sets, and the like to employ a multiplicity of MLCs especially in the power supply circuits associated with intergrated circuit devices. While MLCs have a number of other uses, a high percentage are employed as damping devices to dampen pulses generated in the power supply circuitry associated with I.C. devices, memory chips and the like.
MLCs typically comprise a multiplicity of thin layers of ceramic dielectric material with interposed layers of electrode material. In power supply cicuitry electrodes of opposite polarity are connected across the input power supply terminals of the devices to perform the pulse dampening effects noted.
Despite the advances in automated MLC manufacturing techniques, there still exists the possibility of a short circuit developing between electrodes of opposite polarity. Such short circuit may result from the deformation of the ceramic material under heating conditions with resultant distortion and contact between adjacent electrode layers. Additionally, mishandling of the capacitor in the course of processing is a further possible cause of such short circuiting.
In the event of capacitor failure due to short circuiting, there may result a large and uncontrolled electrical flow which causes damage to associated components in the electronic device such that the damage done to the device is difficult to diagnose and costly to repair.
Additionally, as will be readily recognized to those skilled in the art, the capacitance of a given MLC should be selected in accordance with the circuit requirements. In view of the wide variety of circuit parameters, manufacturers of MLCs are compelled to provide a wide range of capacitor values, such procedures involving variations from value to value in terms of the number of layers embodied in the capacitor, the size and configuration of the electrode areas, and the size and configuration of the monolithic ceramic device proper. Since in large measure, the application of multi-layer capacitors to printed circuit boards is an automated procedure, and since the apparatus employed for positioning the capacitors must be adjusted in most instances where the size of the multi-layer capacity varies, it is highly desirable to provide a constant sized capacitor body the capacitive value of which can be varied to assume a desired figure. It would be further appreciated to be desirable, to provide a capacitor which, in the event of failure, will fail in an "open" condition rather than a shorted condition.
It would be further appreciated by those skilled in the art, to be desirable to provide a capacitor which, in the event of a shorting between adjacent layers will still function to provide a capacitive value in the circuit, rather than merely forming an open circuit or a short between adjacent electrode layers.
2. The Prior Art
Various means have been suggested to eliminate or minimize the damages which may flow as a result of the shorting between capacitor layers of opposite polarity. By way of example, it has been proposed to provide a fuse combined with a monolithic ceramic capacitor (U.S. Pat. Nos. 4,107,759 and 4,193,106). Other examples of fuses embodied in or combined with capacitors of various sorts may be found in the following U.S. Pat. Nos.: 2,216,558; 3,579,062; 2,216,559; 3,368,083; 2,704,341; 4,107,762; 3,236,976; 4,150,419; 3,249,835; 4,186,417; 3,579,061; 4,442,473.
As an alternative to the approach of the above reference patents, it has been suggested to embody a fuse in the printed circuit devices to which the capacitor is connected. Representative examples of prior art patents adopting such approach are U.S. Pat. Nos.: 3,500,276; 4,072,976; 3,699,395; 4,342,977; 4,042,950; 4,394,639.
The fusing devices as represented by the above noted patents have not achieved significant commercial acceptability due principally to the complex manufacturing procedures required for the fabrication of the fused devices.